The BioCycle Study was a prospective cohort study of menstrual cycle function among 259 regularly menstruating, healthy, premenopausal volunteers aged 1844 years from western New York State conducted from 2005-2007. Women were not using hormonal contraception and were followed for one (n=9) or two (n=250) menstrual cycles with fasting morning blood samples collected in each cycle during early menstruation, mid- and late-follicular phase, two days around expected ovulation, and early, mid-, and late luteal phase. The study was very successful with 94% of women completing at least 7 of 8 clinic visits per cycle. The primary findings of this observational study were published in 2010 and described an independent positive association between F2-isoprostane levels and estradiol, a result which called into question the commonly held hypothesis that endogenous estradiol reduces oxidative stress. Since completion of the study, much progress has been made in the analysis of the BioCycle Study data. To date, almost 80 papers have been published. The BioCycle Study has contributed substantially to the fields of nutritional, environmental, and social epidemiology, offering valuable insights into various factors associated with premenopausal womens reproductive and cardio-metabolic health. In particular, several dietary factors have been evaluated with regard to their associations with reproductive hormones and ovulation, including serum antioxidants (Mumford et al. Journal of Nutrition 2016), serum caffeine (Schliep et al. American Journal of Clinical Nutrition 2016), and dietary fat (Mumford et al. American Journal of Clinical Nutrition 2016). These findings have highlighted the important role of diet in reproductive function. Further research evaluating potential environmental factors, including urinary phenol and paraben metabolites, found that these markers were variable across two months in healthy women, highlighting that additional biospecimens may be needed to characterize exposure for certain compounds (Pollack et al. Environmental Research 2016). In addition, it was also observed that medication use (Johnson et al. Pharmacoepidemiology and Drug Safety 2016) and protein intake (Gorczyca et al. European Journal of Nutrition 2016) vary across the menstrual cycle. Further research into the mechanisms driving these associations is needed to understand the potential implications for womens health. Overall, this body of work has been influential in describing not only the short-term impact of diet and lifestyle on hormonal function and markers of menstrual cycle dysfunction (e.g., anovulation, luteal phase deficiency, and abnormal menses) but their potential long-term impact on chronic disease risk. The team intends to build upon its current findings from the BioCycle Study to fill critical research gaps in its quest to answer important public health questions for women of reproductive age.